Endovascular aortic repair (EVAR) is a type of endovascular surgery used to treat pathology of the aorta. The most common EVAR treatment is of an abdominal aortic aneurysm, but many different types of aortic pathologies are treated by EVAR. When used to treat thoracic aortic disease, the procedure is then specifically termed TEVAR (thoracic endovascular aortic/aneurysm repair). The procedure involves placement of an expandable stent-graft within the aorta to treat the aortic disease without operating directly on the aorta. In 2003, EVAR surpassed open aortic surgery as the most common technique for repair of abdominal aortic aneurysm, and in 2010, EVAR accounted for 78% of all intact abdominal aortic aneurysm repair in the United States.
The procedure is carried out in a sterile environment under x-ray fluoroscopic guidance by a vascular surgeon, cardiac surgeon, interventional radiologist, general surgeon, or interventional cardiologist. The patient's femoral arteries are generally accessed percutaneously, e.g., with a surgical incision or direct puncture in the groin. Vascular sheaths are introduced into the patient's femoral arteries, through which one or more guide wires, catheters, and the stent-graft are introduced. The stent-graft acts as an artificial lumen for blood to flow through, thereby substantially isolating the aneurysm sac from direct blood flow and blood-pressure and thereby preventing further enlargement and rupture. The stent-graft is compressed into a catheter, introducer sheath, or other delivery system that allows the compressed stent-graft to be introduced from the femoral arteries to the intended place of deployment.
A stent-graft is typically an assembly of a fabric material and a metal frame or metal springs/stents and mounted on a catheter assembly. When introduced into the vasculature, stent-grafts are constrained to a smaller diameter to enable introduction by different techniques, such as a constraining sleeve or by loading into an introducer sheath. Stent-grafts, stents, and their catheter assemblies are typically produced, constrained, packed and, sterilized under room-air conditions. Consequently, spaces within a constraining sleeve or sheath that are not filled by the stent-graft or stent and/or the catheter assembly generally contain room air. For sterilization, the assemblies are packed in packaging, which is permeable for gas and are sterilized, e.g., using vacuum with ethyleneoxide-containing gas. The gas is removed by repeated vacuum and room air ventilation as a later step of the gas-sterilization process. Thus, when the product is delivered in its sterile packaging there is generally air present within the stent-graft assembly.
In the operating theatre, the stent-graft assemblies are unpacked from their packaging under sterile conditions. Air is removed from some stent-grafts and their catheter assemblies prior to introduction into the vasculature typically by flushing the sheath with isotonic solutions such as saline introduced through flushing ports that are part of the catheter assemblies. Stent-grafts that are constrained using a sleeve, such as the Gore TAG and cTAG device, are typically introduced into the vasculature without flushing to remove the room-air from the assembly.
It is well recognized that deployment of stent-grafts in the thoracic aorta involves a significant risk for stroke. It has been reported to be as high as 10% and is a major drawback of TEVAR.
While retrospective studies have been done, the pathomechanism of stroke as a complication of TEVAR is not well known. Generally, the main source for strokes are thought to be embolism by particles from thrombotic and atherosclerotic material adherent to the aortic wall, which is released by manipulation during deployment by wires, catheters, sheaths and the stent graft. The release of trapped gas or gas mixtures, e.g., air or nitrogen, from the stent-graft during TEVAR may form emboli and/or be a significant pathomechanism for cerebral emboli leading to stroke despite flushing techniques; however, it has been difficult to detect such event cascades since released gas or gas composites are not visible and a stroke attributed to gas embolism may only first be recognized after the patient has woken up.
The risk of air-embolism and stroke during open surgery is well known and preventive strategies have been employed, e.g., in open cardiac surgery and neuro-surgery. Preventive strategies to avoid the introduction of air within endovascular devices into the human body include extensive saline flushing to mechanically squeeze out the air, which is present in catheters, stents (uncovered metal stents), coils, and other devices prior to introduction of these devices into the patient's vasculature. Such flushing with saline generally works well in these applications as air may be removed almost completely; therefore, such flushing is generally part of the instructions for use of these devices.
With stent-grafts (prosthetic vascular grafts supported by metal stents), flushing with saline solution may not work well to remove air prior to introduction into the body. However, it is the method that is widely recommended and used today in most procedures. Because stent-grafts are combinations of stents with a fabric-covering, traditional mechanical flushing with saline may not work well because the fabric significantly hampers the ability to completely drive out the air. Also, factors like the degree of compression may influence the amount of “trapped air.”
Another factor is the presence of side-branches and other advanced tools in modern stent-grafts and their delivery-systems, which may create additional pockets where air may be compressed during flushing, but not squeezed out. During the procedure, the trapped air may then be released during intravascular deployment but may not be visually recognized during the procedural step since air is not typically visible under fluoroscopy, which is generally used for such procedures. The released air may become visible on postoperative CT-scans after EVAR for abdominal aortic aneurysms in the aneurysm-sac days after the procedure, e.g., as shown in FIG. 1. Such occurrences are largely ignored because this air does not seem to cause much harm and is expected to be resorbed within weeks.
Trapped air may also be released when stent-grafts are deployed in segments of the aorta, which are close to brain-supplying arteries or the aortic trunk vessels, e.g., the innominate artery, left common carotid artery, and left subclavian artery. When such trapped air is released, there is a risk of air embolization into the brain. Thus, insufficient removal of air from stent-grafts and/or their delivery systems before they are introduced into the vasculature may be a significant source of stroke during TEVAR. Additionally, a related situation applies if stent-grafts are released close to the coronary arteries, which gives rise to a risk for myocardial infarction due to air-embolization into the coronary arteries.
Air is also known to be released from other medical devices used in neuroradiological procedures. For example, stents and coils and their delivery-assemblies, which are introduced in the arteries of the brain, may also contain air, which may potentially cause damage in the brain. In addition, there is significant stroke risk associated with transcatheter aortic valve implantation (“TAVI”) and current measures, e.g., introducing filters, deflectors, and the like into the patient's vasculature during the procedure, may be ineffective at capturing air or other unwanted gases.
Accordingly, devices and methods that facilitate removing air or other gases from medical devices, particularly stent-grafts, stents, coils and their delivery systems, to reduce the risk of embolism would be useful.